“o-tagai ni / ~au” Meaning & Usage — Each Other / Mutually [JLPT N3]

Content by NTJ Kuma · Nihongo to Japan editorial team · Updated July 27, 2026

Expressing that both sides do something to each other, plus the ~合う pattern — with examples. (JLPT N3)

「お互いに協力する」 — 「お互いに・〜合う」, mutually, each other

「チームでは、お互いに協力し合うことが大事だ」 (on a team, cooperating with each other matters) — 「お互いに」 is an adverb meaning “each other, mutually”; 「verb ます-stem ＋ 合う」 also means “(doing) to each other” (助け合う = help each other). The core is “back-and-forth, two-way.” This guide covers 「お互いに／〜合う」's attachment and that “mutuality,” and separates it from 「一緒に／互いに」 (and warns against confusing 「合う」 with 「会う」).

Core: the action is “back-and-forth, two-way”

The core of 「お互いに・〜合う」 is “mutuality” — not one-sided A-to-B, but A and B each doing the same action to the other:

• お互いに (adverb): お互いに尊重する (respect each other).
• verb ます-stem ＋ 合う: 助け合う (help each other), 理解し合う (understand each other), 譲り合う (yield to each other).

Feel: “two-way, reciprocal” — both do it to the other, not one-way.

How to Connect

Examples in use

• チームでは、お互いに協力することが大事だ。(On a team, cooperating with each other matters.) — adverb
• 夫婦はお互いに譲り合うことが大切だ。(A couple yielding to each other matters.) — 合う
• 困ったときは、助け合いましょう。(When in trouble, let's help each other.) — 合う
• 二人は長年、支え合ってきた。(The two have supported each other for years.) — 合う
• 「ありがとう」「いえ、お互い様ですよ」(“Thanks.” “Not at all — we're even.”) — idiom

⚠️ Where learners slip up

① 「〜合う」 takes the ます-stem, not the dictionary form. ✗ 助けるあう → ✓ 助け合う (助けます→助け ＋ 合う). 「合う」 attaches to a verb's ます-stem (drop ます), not the dictionary form. 話す→話し合う, 理解する→理解し合う, 支える→支え合う.

② Don't confuse the kanji: 「合う」 (match/mutual) vs 「会う」 (meet). Same reading (あう), different meanings! 「合う」 = match, mutual (助け合う = help each other, 目が合う = eyes meet); 「会う」 = meet, see (a person) (友達に会う = meet a friend). The compound verbs for “mutually …” use 「合う」 (話し合う = discuss), not 「会う」.

③ 「お互いに」 (mutually, two-way) vs 「一緒に」 (together, doing jointly). お互いに = each to the other (two-way, reciprocal) (お互いに助ける = you help me, I help you); 一緒に = two people doing the same thing together (side by side, at once) (一緒に勉強する = study together — toward the same goal, not necessarily to each other). For “mutually, back-and-forth” use お互いに; for “together, jointly” use 一緒に.

🔄 Compare with similar forms: お互いに／一緒に／互いに／し合う

💡 How to remember this

The core of 「お互いに・〜合う」 is “mutuality — back-and-forth, two-way, reciprocal”: お互いに (adverb: お互いに尊重する = respect each other), verb ます-stem ＋ 合う (助け合う = help each other, 理解し合う = understand each other). It stresses “not one-way, but both doing it to the other.” Three points: ① 〜合う takes the ます-stem (助け合う, ✗ 助けるあう); ② use the kanji 「合う」, not 「会う」 (合う = mutual/match, 会う = meet); ③ separate it from 「一緒に」 — お互いに is “mutual (you help me, I help you),” 一緒に is “together (side by side).” The idiom 「お互い様」 (we're even, same for both) is handy too. For the reciprocal give-and-take of teamwork and mutual support, this set is spot-on.

❓ FAQ

Q: How do I tell 「お互いに」 from 「一緒に」?

By “mutual (two-way)” vs “joint (side by side).” 「お互いに」 = each to the other (mutual, two-way, back-and-forth): お互いに助け合う (help each other — I help you, you help me, two-way), お互いに理解する (understand each other — I get you, you get me), お互いに謝った (the two apologized to each other). It stresses “the action is two-way, A to B and B to A.” 「一緒に」 = together, jointly (two people doing the same thing side by side, in the same direction): 一緒に勉強する (study together — each studies, but together), 一緒に旅行する (travel together), 一緒に歌う (sing together). It stresses “doing jointly, not necessarily to each other.” So: “mutual, back-and-forth (A to B, B to A)” → お互いに; “together, side by side (A and B do X together)” → 一緒に. E.g., 「お互いに教え合う」 = teach each other (I teach you, you teach me); 「一緒に勉強する」 = study together (each on their own, just together). One is interaction, the other joint action.

Q: How does the verb before 「〜合う」 attach? What's the difference between 「合う」 and 「会う」?

Attachment: 「〜合う」 takes the verb's 「ます-stem」 (＝ ます-form minus ます): 助けます→助け ＋ 合う = 助け合う (help each other), 話します→話し ＋ 合う = 話し合う (discuss, talk over), 理解します→理解し ＋ 合う = 理解し合う (understand each other), 支えます→支え ＋ 合う = 支え合う (support each other). ✗ 助ける合う, ✗ 話す合う (can't attach the dictionary form). 「合う」 vs 「会う」: both read 「あう」, but mean entirely different things: 「合う」 = match, fit, mutual (味が合う = suits one's taste, 目が合う = eyes meet, 話し合う = discuss, 助け合う = help each other); 「会う」 = meet, see (someone) (友達に会う = meet a friend, 駅で会う = meet at the station). The compound verbs for “mutually …” (〜し合う) always use 「合う」 (the “mutual” sense), not 「会う」. Mnemonic: 〜合う takes the ます-stem, kanji 「合」 (mutual), not 「会」 (meet).

🖊️ Practice Questions (5)

Q1. 「チームでは、___協力することが大事だ。」(cooperating with each other)

(A) お互いに　(B) わざと　(C) せっかく　(D) もともと

Q2. 「助ける」を「helping each other」にすると?

(A) 助け合う　(B) 助けるあう　(C) 助けてあう　(D) 助かり合う

Q3. 「お互い様」の意味は?

(A) We're even / same for both of us (mutual)

(B) Only me

(C) Only you

(D) None of these

Q4. 「〜合う」の前に来る動詞の形は?

(A) ます形語幹

(B) dictionary form

(C) た形

(D) て形

Q5. 接法が正しいのは?

(A) 励まし合う。　(B) 励ます合う。

(C) 励まして合う。　(D) 励ました合う。

Answer Explanations

1. (A) お互いに ── Cooperating with each other.

2. (A) 助け合う ── ます形語幹＋合う.

3. (A) ── We're even (same for both).

4. (A) ます形語幹 ── 〜合う takes the ます形語幹.

5. (A) ── 励まし (ます形語幹) ＋合う.